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MICROBIOLOGICAL STUDIES ON THE ANTIBIOTIC TOLERANCE OF NON-REPLICATING MYCOBACTERIUM ABSCESSUS: EFFECTS OF EFFLUX PUMP INHIBITORS AND METABOLIC ENERGY SOURCES
Mycobacterium abscessus is an emerging infectious pathogen capable of causing pulmonary disease similar to tuberculosis, but has many intrinsic and extrinsic properties making it more drug-resistant than Mycobacterium tuberculosis. Current treatments, including those used for M. tuberculosis infection, have had poor results. Although in vitro studies have shown promise with drug treatment for this microorganism, clinical trials have been mostly unsuccessful. An in vitro model that mimics the physiological stresses encountered within the human body is likely to enable the discovery of mechanisms of antibiotic resistance used by M. abscessus during infection. Therefore, we subjected M. abscessus to a combination of stresses thought to be encountered by mycobacteria inside the human body. We subjected the pathogen to low oxygen, low pH, and nutrient starvation. This is the first report on subjecting M. abscessus to such a combination of stresses. It is also the first to investigate the effect of the combination of stresses on the tolerance of the pathogen to antibiotics, and the effect of efflux pump inhibitors under such conditions. We found that under these conditions, M. abscessus entered a non-replicating state. We investigated whether the multiple-stressed M. abscessus displayed altered tolerance to antibiotics commonly used to treat infection, and whether efflux pump inhibitors affected the antibiotic resistance under such conditions. We found that when subjected to our multiple stress model, M. abscessus in the reactivating phase had higher tolerance to erythromycin in combination with efflux pump inhibitors verapamil and reserpine compared to non-replicating M. abscessus. Reactivating phase cells had a higher tolerance to antibiotic erythromycin than non-replicating cells. Reactivating phase cells also showed antibiotic tolerance in the presence of ATP. This physiologically-relevant experimental model for M. abscessus could potentially be used in discovering the mechanisms of antibiotic resistance in the pathogen.